1. Field of the Invention
This invention relates to an observation device, using a plurality of microscopes for observing a plurality of mutually adjacent regions on at least two objects, which are superposed on each other with respect to the direction of an optical axis.
2. Description of Prior Art
The type of observation device, to which the subject invention relates, may be employed, for example, in the (1) aligning and cementing, with good positional accuracy, a tri-color separation filter such as a stripe filter, etc. onto a solid-state imaging device chip such as a CCD chip of from a few millimeters square to ten or greater millimeters square, or in (2) carrying out an alignment operation before contact, or proximity printing of a mask of the same size as mentioned above onto a very small wafer made of a special crystal such as GaAs, etc. that cannot easily be produced larger than 20 mm square due to difficulty in producing a large crystal. However ordinary silicon wafers can be made as large as three to five inches in diameter).
The above-mentioned alignment operations should be done in such a manner that both chip and filter, or both mask and wafer, be aligned with each other with a positional accuracy of one micro-millimeter or less over the entire surfaces of these objects. In particular, since the accuracy should be maintained over the entire surfaces, the positioning operation should be done by observing a plurality of locations (usually two places on both left and right) of the objects. As mentioned in the foregoing, however, the above-mentioned chips or wafers are 20 mm square at the largest, so that the observing points on the objects are separated by 20 mm at the most. It is impossible to dispose a plurality of microscopes in this narrow space interval. Particularly, when the accuracy required in positioning objects becomes higher, the microscopes are required that have high image resolution, and lenses of high resolution should inevitably have a large aperture, which, in turn, tends to increase the diameter of the lens barrel. On account of this, it becomes all the more difficult to dispose the microscopes in such a narrow space interval. For instance, when the positioning accuracy is determined at one micro-meter or less, a numerical aperture (N.A.) of an object lens in the microscope is required to be 0.2 and above, and when the working distance is set at 20 mm, the lens barrel of the object lens becomes as large as 20 mm and above with the consequence that it is impossible to observe two object points at an interval of less than 20 mm.
FIGS. 1A and 1B of the accompanying drawing illustrate an apparatus and method for observing two adjacent regions, which might be devised most easily.
In the drawing, a reference numeral 1 designates a CCD chip, and a reference numeral 2 designates a tri-color separation filter. These CCD chip 1 and the color filter 2 are superposed on each other with respect to the optical axis of a microscope 3.
In the state shown in FIG. 1A, the right end of the chip 1 and the color filter 2 are observed for alignment. Subsequently, the chip 1 and the color filter 2, as an integral whole, are shifted to the right direction in the drawing, or the microscope 3 is moved to the left direction, as shown in FIG. 1B, so that the left end of the chip 1 and the color filter 2 may be observed for alignment. By repetition of this operation a few times, both chip 1 and color filter 2 can be aligned with satisfactory accuracy over their entire surfaces. This method, as is understandable from the above description, takes time to achieve the positioning, and therefore cannot be said to be an entirely satisfactory solution to the problem.
An alternative apparatus and method might be suggested in which two microscopes 3, 3 are disposed with their object lenses inclined to the surface of the chip 1 and the color filter 2, with a line perpendicular thereto as the axis of symmetry. While this apparatus has an advantage of reducing time for the positioning operation in comparison with the previously described apparatus and method, it still has a problem of accuracy in positioning the objects because the object surface is observed from a inclined direction. Therefore, this apparatus and method, too, cannot be said to be entirely satisfactory for solving the problem.